For many years, the most widely used technique for purifying large quantities of water has been the addition of small quantities of chlorine or chlorine releasing compounds to the water, sufficient to destroy undesirable micro-organisms. Chlorination has however the disadvantages firstly that it tends to render the water less acceptable for drinking or bathing, particularly if the chlorine concentration and pH of the water are not carefully controlled, and secondly that the chlorine may interact with other compounds present in the water to leave low concentrations of possibly harmful chemicals.
It has been known for many years that ultraviolet light at appropriate wavelengths has powerful germicidal properties, and the use of ultraviolet light for water purification purposes has been gaining in popularity in recent years since it avoids the disadvantages associated with chlorination. The problems associated with such treatment are mainly problems of implementation, i.e. ensuring adequate irradiation of large quantities of water in an effective and energy efficient manner, using equipment which is readily and economically maintained.
One type of equipment which has found favour uses a battery of parallel elongated ultraviolet tubes supported on appropriate carrier frames in a channel through which the water to be treated is caused to flow. The spacing of the tubes from each other and from the walls of the channel is such as to minimize the path of the ultraviolet radiation from the tubes through the water. An example of such an arrangement is shown in U.S. Pat. No. 3,948,772.
As the number of tubes utilized in an installation increases, it becomes increasingly essential that adequate provision be made for replacing tubes as and when they fail. One approach to this problem is disclosed in U.S. Pat. No. 4,482,809 (Maarschalkerweerd) issued Nov. 13, 1984. This patent discloses an arrangement in which groups of vertically adjacent tubes are supported in individual rack assemblies which can be withdrawn from a treatment channel for replacement of tubes. In the arrangement described in this patent, the lamps are housed in transparent tubes extending between sockets integral with the side arms of a rigid frame, at least one of the sockets having an end plug through which a lamp can be withdrawn longitudinally once the frame has been withdrawn from the channel. This arrangement is relatively complex to fabricate, and while it may appear an advantage that the lamps are rigidly secured in the frame, this entails that any distortion of the frame during handling strains the quartz tubes containing the lamps, thus risking breakage. Furthermore, considerable attention must be paid to leak-proofing, since any leak may penetrate throughout the assembly.
A further problem with such assemblies is that they are commonly required to accommodate widely varying rates of water flow, which means that the degree of irradiation will vary according to the rate of flow unless some means is provided to compensate for this effect.
Finally the use of electrical equipment in a wet environment, and the use of high intensity ultraviolet radiation, poses safety hazards against which the operators of the plant should be protected. In particular, there should desirably be some positive assurance that power is disconnected from the assemblies before they can be removed from the channel, since this both inhibits disassembly in a powered up condition, and ensures that radiation ceases before an assembly is removed.
It is an object of the present invention to tackle the above problems. In a first aspect, the present invention provides in a water treatment plant comprising a treatment channel for the passage of water to be treated, at least one array of parallel elongated ultraviolet electric lamp units, means for supporting said at least one array with the channel, and means for connecting said array to an electrical power supply, the improvement wherein each lamp unit in the array comprises an individually watertight assembly of a tubular ultraviolet lamp, a tubular housing for the lamp which is transparent to ultraviolet radiation, and watertight end cap units for the tube, at least one being removable and which establish electrical connections to the lamp, and the lamp units are assembled into arrays by releasably engaging the assembled units between end bars of a frame, said end bars releasably engaging opposite end caps of each assembled unit. Preferably the end bars have series of spaced sockets between which the lamp units are removably located, each end cap of a lamp unit comprising a locating spigot releasably engageable with locating means on an end bar so as to require removal of that end cap from the frame before the lamp unit can be disassembled.
The end bars may be connected by braces extending parallel to the lamp units to provide a frame which may be suspended from spaced hangers of a rack supported above the channel. Preferably the frame mounts a multiple connector plug establishing electrical connections between the lamp and a complementary socket mounted on the rack and connected to the power supply, such that the frame cannot be removed from the rack without withdrawing the plug from the socket. In a preferred arrangement, the frame must be moved horizontally on the rack to disengage the plug from the socket before it can be lifted upwardly from the channel.
The invention also extends to the provision of, in an ultraviolet water treatment plant comprising a treatment channel for the passage of water to be treated, at least one vertically stacked array of elongated ultraviolet electric lamp units, means for supporting said at least one array within the channel, and means for connecting the lamps of said array individually to a power supply, the improvement wherein means are provided to restrict the flow of water through the channel such that the depth of water in the channel, and hence the number of lamps in each said array which are immersed, is progressively increased in accordance with the rate of flow through the channel, means to sense the depth of water in the channel, and switching means associated with said power supply and controlled by said sensing means to turn on only such lamps as are required to irradiate the water.
Preferably the means to restrict the flow of water through the channel comprises a weir assembly comprising an upper barrier portion, spanning the channel, and having an upper edge forming a weir, and a lower sluice portion hingedly suspended from the lower edge of the upper barrier for swinging movement in a downstream direction and biased towards a position in which it closes the channel beneath the upper barrier. As the water level upstream of the weir assembly increases the sluice firstly opens progressively to permit an increasing flow of water, and then the rate of flow through the fully opened sluice increases as the level of water behind the barrier increases. Finally the water pours over the weir at increasing rates as its level further increases.
Further features of the invention will become apparent from the following description of a preferred embodiment with reference to the accompanying drawings.